In the lithographic printing process, a lithographic plate comprising an aluminum sheet is initially coated with a photosensitive layer. A negative is applied over the photosensitive layer, after which the lithographic plate having the negative applied thereto is exposed to high intensity light. The negative is then removed, and the plate is fed into a lithographic plate processor.
In the processor, developer is initially applied to the exposed surface of the plate and is then spread across the entire exposed surface. A developer apparatus then distributes the developer on the exposed surface. Next, the exposed surface is washed to remove excess developer. A layer of gum arabic is then applied to the exposed surface, after which the lithographic plate may be dried.
Following the processing operation, the lithographic plate is ready for use in a conventional lithographic press to effect printing. In the press, ink is applied to the plate by means of a roller. The plate is then utilized to print on a blanket, which is in turn used to print a plurality of sheets formed from paper or other material in the conventional manner.
The present invention relates to an improved developer apparatus for lithographic plate processors, and more particularly to a developer apparatus which simulates the results obtained by means of manual developing techniques. It has heretofore been known to utilize in a lithographic plate processor a developer apparatus comprising a large sponge which is moved laterally as the lithographic plate passes thereunder. Such a device does not achieve satisfactorily uniform developing over the exposed surface of the plate, which in turn results in poor quality lithographic prints. Thus, a need exists for an improved developer apparatus for use in lithographic plate processors, and in particular for a developer apparatus capable of duplicating the results heretofore obtainable only by means of manual developing.
In accordance with the broader aspects of the invention, a developer apparatus for use in lithographic plate processors comprises a plurality of developer members positioned for engagement with the exposed surface of a lithographic plate. Structure is provided for rotating the developer members about spaced axes each extending substantially perpendicularly to the plane of the exposed surface of the plate. Simultaneously with such rotation, all of the developer members are oscillated relative to the path of movement of the lithographic plate, thereby developing the exposed surface of the plate in a substantially more uniform satisfactory manner than has been possible to achieve heretofore other than manually.
In accordance with more specific aspects of the invention, the developer members comprise rectangularly shaped members and are mounted for rotation about overlapping circles. In one embodiment of the invention the developer members comprise sponges formed from nylon or the like and mounted for engagement with the exposed surface of the lithographic plate. In accordance with another embodiment of the invention the developer members comprise brushes formed from nylon or the like and positioned for engagement with the exposed surface of the lithographic plate.
In accordance with still other aspects of the invention, the developer members are rotatably supported on a subframe. The subframe also supports a drive mechanism which functions to simultaneously rotate all of the developer spreader members. Structure is provided for oscillating the subframe in a direction extending substantially transversely to the direction of lithographic plate movement concurrently with the rotation of the developer members. By means of the simultaneous rotation and oscillation of the developer members, the present invention functions to develop the exposed surface of a lithographic plate in a highly uniform and superior manner.